OLEDs have been the subject of a considerable amount of research in recent years because of their use and potential use in a wide variety of electroluminescent devices, and are now reaching commercialization. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting applications or flat-panel display applications (e.g., OLED displays). OLED displays are known as being very bright and having a good color contrast and wide viewing angle. However, OLED displays, and in particular the electrodes and organic layers located therein, are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. It is well known that the life of the OLED display can be significantly increased if the electrodes and organic layers within the OLED display are hermetically sealed from the ambient environment. Unfortunately, in the past it was very difficult to develop a sealing process to hermetically seal the OLED display. Some of the factors that made it difficult to properly seal the OLED display are briefly mentioned below:
The hermetic seal should provide a barrier for oxygen (10−3 cc/m2/day) and water (10−6 g/m2/day).
The size of the hermetic seal should be minimal (e.g., <2 mm) so it does not have an adverse effect on size of the OLED display.
The temperature generated during the sealing process should not damage the materials (e.g., electrodes and organic layers) within the OLED display. For instance, the first pixels of OLEDs which are located about 1-2 mm from the seal in the OLED display should not be heated to more than 100° C. during the sealing process.
The gases released during the sealing process should not contaminate the materials within the OLED display.
The hermetic seal should enable electrical connections (e.g., thin-film chromium) to enter the OLED display.
Today, one method for sealing the OLED display is to use different types of epoxies, inorganic materials and/or organic materials that form the seal after they are cured by ultra-violet light. For example, some seals use a composite-based approach where alternate layers of inorganic materials and organic materials can be used to seal the OLED display. Although these types of seals usually provide good mechanical strength, they can be very expensive and there are many instances in which they have failed to prevent the diffusion of oxygen and moisture into the OLED display. Another common way for sealing the OLED display is to utilize metal welding or soldering. However, the resulting seal is not durable in a wide range of temperatures because of the substantial differences between the coefficients of thermal expansions (CTEs) of the glass plates and metal in the OLED display.
More recently, glass-based frits have been used to seal glass substrate plates in a glass package that provides excellent hermeticity to the enclosed device. But many of these frits contain toxic elements, such as antimony, which pose environmental hazards. There is a need for a glass-based frit suitable for hermetically sealing glass packages, such as electronic devices (e.g. for display-type applications), having a low coefficient of thermal expansion (CTE) that does not contain antimony.